Many load sense hydraulic systems use a common load sense pump for both the steering circuit and the implement circuits and include a priority valve for ensuring that the steering circuit demands are satisfied before flow is made available to the implement circuits. The priority valve typically controls the pressure and flow to the steering circuit in response to a load sense signal from a steering control valve such as a hand metering unit (HMU). The load sense signal in some steering circuits is referred to as dynamic because oil from the pump flows through a load sense signal line, the priority valve and a tank path in the HMU when the HMU is in its neutral position. Operating the HMU to initiate a steering maneuver causes the pump to upstroke to system pressure by diverting the dynamic oil flow from the tank path to the steering control pressure circuit.
In one hydraulic system, a load sense pressure reducing brake valve is connected to the pump upstream of the HMU to provide oil to a brake circuit. The load sense signal port of the brake valve was connected to the signal line between the HMU and the pump control to upstroke the load sense pump when the brake valve was actuated. However, one of the problems encountered therewith under some operating conditions was that the brake valve could not generate the combination of flow and pressure to control the priority valve resulting in the brake feeling the interaction with the steering and implement functions.
Thus, it would be desirable to integrate the load sense pressure reducing brake valve into the dynamic load sense steering circuit in such a way that brake valve response is improved and interaction with other circuits is reduced or eliminated.
The present invention is directed to overcoming one or more of the problems as set forth above.